What is the value of a coin that has been struck offcenter?

I have a number of pennys that have all been mis-struck. One is a coin blank, two have been hit almost half off the coin, and one has the reverse of another coin pressed into it's obverse side. I know that the exact value can't be determined without seeing the actual coin but I was wondering if they could be worth anything more than a dollar or two.

Error coins are "hot," and "ultra-rare" at least according to a small community of numismatic scammers. Beware of these folks. For example: An ebayer recently was selling mis-struck Canadian coins for $300.00 each, while collectors were selling the same error coins for about $3 because the small error is actually extremely common. They were toonies ($2 coins). To the rest of us, error coins are fascinating and can reveal a lot about the coin minting process. They can be very rare or very common, depending on who made them, where they were made, when they were made, how many were made, and what caused the problem. There could be some good value in your coins depending on the type and severity of the error, the rarity, the grade, and a number of other factors. It could also be just a curiosity piece of small value. In other words, I suggest you take your coins to a reputable appraiser and have them examined. I advise against simply using a web-search for "error coins" as it is, like I said, a hot topic for scammers. Without knowing more, I'll have to guess that the value will be low. $5 tops, and more likely under $2. Still, there is a small chance, one worth investigating, that the coins could be worth a pretty penny. Pardon the pun.

Oh, the one with the incorrect die (another coin pressed on it) is quite possibly the most valuable of the collection and most likely to be worth a significant amount. The offset pennies are common for some years, rare for others, values don't often get high but if it's really "bad" it could be valuable. Coin blanks are usually valuable strictly for educational purposes and I simply suggest keeping that one in your collection.